The present invention generally relates to batteries having one or more electrochemical cells. The present invention further generally relates to batteries including an electrochemical cell having a spiral-wound electrode assembly in which the positive and negative electrodes of the electrochemical cell are wound about a mandrel in a spiral manner.
Batteries are known that include an electrochemical cell in which the positive and negative electrodes are wound into a spiral-wound electrode assembly (also known as a jelly roll assembly). The positive and negative electrodes in these types of batteries are typically constructed of elongated conductive foil strips made of aluminum or copper that have a mixture of materials including active electrochemical materials coated on both sides. The positive and negative electrodes are wound by a mandrel with layers of a separator material disposed between the electrode layers so as to prevent any physical contact between the positive and negative electrodes. After the spiral-wound electrode assembly has been wound about the mandrel, the spiral-wound electrode assembly is removed and inserted into an open end of a cylindrical or prismatic metal cell housing. Subsequently, an electrolyte is dispensed into the open end of the cell housing. The liquid electrolyte flows around and within the spiral-wound electrode assembly and is absorbed into the separator layers between the positive and negative electrodes so as to enable the transport of ions between the positive and negative electrodes.
After the electrolyte has been dispensed within the cell housing, the cell housing is sealed by inserting a cover assembly into the open end such that the cover assembly is electrically connected to one of the electrodes, and crimping the cell housing to hold the cover assembly in place. The cover assembly is also preferably electrically insulated from the cell housing so that the cover assembly and the cell housing each serve as electrical contact terminals having opposite polarities.
Such spiral-wound electrode-type cells are typically used in combination in rechargeable battery packs for video cameras, cellular telephones, and portable computers. Because battery packs of these types require high output voltages, the cells used typically have cell voltages at or in excess of 3 volts. The components used to construct these electrochemical cells are typically more expensive and require more stable electrolytes and binders, which bind the active electrochemical materials to the conductive electrode strips.
A further problem with the construction of spiral-wound electrode-type electrochemical cells constructed as described above, results from the use of the microporous separators. Such microporous separators are one of the more expensive components of the electrochemical cell. Further, these separators typically increase the internal resistance of the cell and, as a consequence, may decrease the high-rate performance of the cell. Moreover, the separators themselves are not electrochemically active components and consume space within the cell housing that could otherwise be filled with electrochemically active components.
It is known in the art of alkaline batteries to construct a high-voltage battery using a plurality of lower voltage electrochemical cells coupled in series. For example, conventional 9-volt batteries are constructed by coupling six 1.5-volt cells in series. Such multi-cell batteries are typically constructed using electrochemical cells that have separate sealed housings so as to keep the liquid electrolyte contained therein separate from each of the other cells. If the liquid electrolyte were allowed to flow freely between the cells, inter-cell leakage current would result. Because of the space that would be required within the battery housing for including separate sealed cells, such batteries make poor use of the total battery volume. As a result, low-voltage cells are poor candidates for high-voltage battery construction.